The Iron Warriors are one of the nine First Founding Traitor Legions of Chaos Space Marines that turned to the service of Chaos during the Horus Heresy and now fight to overthrow the Imperium of Man. The Iron Warriors, who were originally the IVth Legion of Space Marines, specialised in the breaking of sieges and assaults on static fortifications, which made them great rivals of the Imperial Fists Legion, said to construct the greatest static defences in the Imperium. It was this rivalry between the Legions, and between their primarchs Perturabo and the Imperial Fists' Rogal Dorn, that helped turn the Iron Warriors to Chaos. Like the members of the Adeptus Mechanicus and the Loyalist Iron Hands Chapter, the Iron Warriors have a strong predilection for replacing parts of their body with cybernetic enhancements. When struck with a mutational "gift" from the Ruinous Powers, most Iron Warriors simply cut off the mutated appendage, if possible, and replace it with a mechanical one.